Amstrad CPC 464 Issue

[rsearle]

Hi All, I'm having an issue with an old CPC 464 and was pointed here from the forums on retrogamer.net...



The other day my buddy and I dug out his old Amstrad, booted it up and had a good few games for Wrestlemainia before powering it off for the night, the next day we go to power it up but nothing is displaying on the screen.


The monitor seems to be working (I can adjust the brightness nob and get little bits of interference), all power lights are on, the tape deck is working fine and I can hear the quietest of hisses from the on board speakers. but still nothing showing up on the screen, I've tried a few commands, (that should start the tape deck loading) but nothing.


Has anyone had any experience with these sorts of issues on this machine, or has any ideas what the issue might be? or even a better resource for this type of stuff? I'll literally been searching the web for hours looking for an answer!


Thanks in advanced for any help.


Regards,


Rich

[endangermice]

Hi Rich,

First things first you should check whether the machine is actually working - so power it up and press the delete key a few times - ensure the volume is turned up and you should hear it beeping. If that's the case there is probably a problem with the monitor or connection from the CPC to the monitor.


If the machine doesn't beep then you might have a problem with one of the internal chips - it could have blown or worked it way loose one of the tracks on the board may be faulty or there might be a short circuit in there somewhere.


It could also be a problem with the power switch or the power supply not quite supplying the 5V DC the machine expects.


Since the machine has by the sounds of it been stored away for sometime - I would say it's well worth taking it apart and cleaning it out. Be very careful not to generate any static electricity - using a hoover to clean it out may not be the wisest idea for example since they can create a lot of static. I usually actually wash all of my boards but do spend a good while drying them out afterwards - water will conduct electricity so a wet board powered up could damage a lot of chips!


Do you have any electronics experience...?

[rsearle]

Hey Man,


Thanks for the reply,


I'll try the delete thing when I get home from work tonight, but I do get a feeling its a problem with an internal chip, I done bits of pieces of electronics, I've build PCs and do a lot of Arduino and Raspberry PI projects.


I guess the first steps will be to give it a good old clean, And I'll report my findings later on today,


If anyone else has any more advise I really appreciate it!


Regards,


Rich

[endangermice]

I've just repaired a rather broken 6128 and there are plenty of people on this forum who can give you lots of advice on how to repair the machine.


The first thing you need to do is to asses and report back its current state - just the basics right now i.e. does it get power does it beep when you press the delete key then we can take it from there!


It's relatively easy to get most of the spares for these machines so I'm sure you'll be able to get it fixed - it may be something as simple as a chip that has worked its way loose!

[rsearle]

OK, so here's how the evening has gone so far,


I've tried repeatingly hitting the del key with the sound up full, but I didn't hear any noise coming from the machine, so I decided to just take it apart genteelly and have a little look inside.


To my surprise is wasn't too dusty, and I didn't want to do anything drastic tonight, but I did notice the solder on the joystick pins was looking rather weathered, and the last thing I did before it refused to restart was to unplug a joystick.


If there wasn't a proper connection on the board to the joystick port, would this cause the amstrad not to boot up?


I've uploaded some pictures to imgur, you can see them here : Photo Album - Imgur joystick-port is photo #2


Any Ideas?


Cheers!


Rich

[Badstarr]

Off the top of my head I can't think of any reason why the joystick port would cause a non booting issue (maybe I'm not giving it enough thought though lol!) From having a good look at the photos that you posted links to, the mainboard looks rather well preserved. The only thing I can think that may be worth trying is checking the CPU and GATE ARRAY are properly seated in their sockets. If the machine has not been used for sometime the PCB may have changed relaxed/shape slightly.


There are two ways I would do this, first is to give the Z80 CPU a gentle prod downwards and as evenly as possible across its surface into the socket, but not too hard! This should ensure the IC is seated properly, then power up and see if anything has changed, if not, do the same with the GATE ARRAY (the one under the metal heat sink, you will probably have to remove this first then replace before powering up). Any difference now? If so a small amount of corrosion/dust/residue may have built up in between the IC pins and those of the IC Socket. I would remove the socketed ICs and give them all a careful and gentle clean, I personally use some very fine (1200 grit) wet and dry sandpaper, and a little alcohol on a cotton bud to remove what ever lifts off the pins. Then, when dried ensuring the pins are all straight, gently place the IC back into its socket again ensuring good contact.


I had a fairly stubborn RAM IC in my old Atari ST that would cause the machine to crash if it had not been used for sometime, applying pressure to the IC would solve the problem temporarily when I got sick of doing that or having the odd random crash during use, I tried the process I just described and it's never been a problem since.


If it turns out that the chips are seated correctly and have good cantact it may be that another component is malfunctioning/dead/dry jointed the only way to work this out is by systematically testing examining each component and it's continuity with reference to the mainboard schematics held on the main Wiki page.


Hope you get it going again!

[endangermice]

My comments pretty much echo Badstarr's response. The only was I can think that the joystick could cause the machine not to boot up would be if it is somehow causing a power shortage. Since the CPC doesn't carry the +5v signal in the joystick plug I would say this is incredibly unlikely / impossible in fact, I suspect the worst you'd see is some random characters after the Ready prompt every time you boot the machine up.

Definitely check the socketed chips in the way that has been suggested. If that doesn't help, a light clean of the motherboard would be a good thing to do, particularly check the underside in case something metallic has worked its way in underneath and is causing a short circuit. Believe it or not several years my PC managed to suck in a slither of tin foil which shorted a few components on the motherboard - just enough to stop it from working - it's a rare occurrence but it can happen!

In the case of the 6128 I recently repaired, the problem was a broken track. These can be hard to spot (although the previous owner of mine had gouged out three which were obvious - the fourth wasn't at all since I think the break was somehow hidden under the socket that had been installed). Also a dry or broken solder joint - either not done properly in the factory or something that has just moved with heat expansion over time can cause breaks in connections. Your continuity check will determine this too.

In all of these cases as Badstarr says, the schematic diagram really is your friend. This is easy to follow - though I'd would recommend that you use a notepad too. Generally I figure out which chips are connected to which other chips - write down the name of the signal and then the leg number on chip one and the leg number it should be connected to on chip two. I then run through the list and tick off each one that shows continuity. It's also worth doing your check from the chip pins themselves since if the chip is socketed no continuity here could also mean a problem with the chip socket if you find there's continuity between the solder pads when both pins meet the motherboard.

If you still have no joy then the next thing to do is to check the main chips on the system - if you're unsure about anything, post a message back - there are several members on this forum who have extensive knowledge of both electronics and particularly the hardware of the CPC who will I'm sure be delighted to help!

Damien

[arnoldemu]

I have heard of stories where plugging/unplugging a joystick can cause the ay chip to become broken.
I can't remember if that just stopped it making sound, or if it actually broke it.

[endangermice]

I'd imagine that might happen if you were to shoot a voltage down one of the pins - perhaps possible due to the odd configuration Amstrad has for its joystick port compared to the Atari original spec. Even if the AY chip was knackered the machine should still boot but you may have no sound and maybe a lack of keyboard input.

[Gryzor]

Could the dry/broken joint cause the AY to short somehow?


Also, this suggests, I guess, that there might be other dry joints as well, especially around the power plugs...

[rsearle]

thanks for all the help guys, I'm at work now but I'll attempted some of your suggestions tonight, and report back, I'm guessing it is either a dry / loose joint or a loose chip.


Really Appreciate all the help!


Rich

[Badstarr]

I would think the possibility of blowing something on the AY is extremely remote especially when plugging in a simple device such as a joystick. I think its more likely that the long term storage of the CPC has affected something, more than likely the PCB has warped. Using the CPC for a while and having it at room temperature will cause the PCB to become a little warm and it will effectively relax back into shape, this can cause fragile solder joints to become detached, and an intermittent connection on a few of the ICs on the PCB will start to make things go a little funky.


Besides the potential issues with dry joints etc, there can also be problems with components such as capacitors and resisters turning into dust. Look for tell tale signs such as a chalky calcified looking residue on capacitors and resistors. A lot of people store their old gear in the attic, some may think that this shouldn't cause much problems, after all, it's indoors isn't it? The problem is that the temperature changes can be pretty extreme and this can speed up corrosion.


Although your machine looks remarkably well preserved for the most part, there are some signs that it may have a little corrosion here and there. If this corrosion developed on and around the pins of the socketed ICs then you can imagine how contacts would become dodgy if it shifted position slightly.


I think you will get it running again though after a little investigation.

[endangermice]

Wow Badstarr, that was quick you got right in there just as I was writing a very similar replay    anyway for what it's worth here what I was going to post:

I think a good check of the joints is definitely the place to start as Grayzor says the state of the joystick joint is a potential indication that something else may be amiss especially since it has been sitting unused for so long - the joints etc. contracting when it cooled down may have disconnected something!


Anyway the consensus is - check your joints and socketed chips!

[Badstarr]

Haha! Funny when that happens, usually I find that happens to me! It is good though when it happens in a way as it shows that your ideas are at least considered rational by other people too. The odd thing is though that I typed the reply on my new iPad (I felt I desrved a non CPC treat for a change and its perfect for zipping through the schematics on the wiki!) so I'm rather impressed that I was able to type quick enough! Now what would be really cool is if I could skin the virtual keyboard to resemble a 464!

[rsearle]

Hi All,


A little update, I've taken the machine apart gently and given it a clean with a small brush, after that I tried what Badstarr originally suggested by applying a small amount of force on the CPU and GATE ARRAY and then trying to boot the machine, but no luck, I've also spent a good hour or so going over the tracks looking for breaks but to be honest its looking a pretty good condition, no residue on capacitors or resistors,


I'm wondering if the main board is getting power? as the speakers / tape deck and power lights or on the separate top board, can I test the ribbon from this board with a multimeter to see if its delivering power?


Thanks


Rich

[endangermice]

It can be extremely difficult to see track breaks with the naked eye though on a CPC with a somewhat less dense circuit board it's not as hard as modern systems.

It's well worth checking for power on the board - I'm not hugely familiar with the 464, on the 6128 all of those components plug into the main board - I would have thought there is a connector from the main board to the aux board with power being deliver via a mini din straight to the main board? Also check the schematics for pin assignments (Z80 is pin 11 for vcc and 29 for ground) and see if there's power present at the CPU, Gate Array etc these should all read around 5v DC. If you have a multimeter that can measure frequency, check the clock on the Z80 it's pin 6 so one probe on pin 6 the other on a ground point - you should see 4Mhz or thereabouts.

After that I would consult the schematics again and check all Data and Address bus connections between the CPU, ROM RAM and Gate Array. Unfortunately this has to be done methodically and is not a quick task. If still nothing then we can advise on how to check the different ICs are actually working.

Badstarr I think our update speeds were matched because I typed that post on an IPAD too - great for viewing schematics! I'm typing this one on the train on my IPhone - somewhat challenging!

[Badstarr]

Bah! Sometimes these things are more complicated than you expect them to be. Ok I have just had an other look at the photos you posted and it could be nothing but the pin on the power socket, on the left hand side next to the screw, it looks a little odd to me, but it could just be the way it looks in the photo. Does it look ok in real life? Give the socket a little wiggle, is there any excessive free play? Have you examined the underside of the PCB at all?


Another thing that has worked for me in the past is, with the system completely powered down, work the power switch back and forth several times don't go mad with it just apply about the same force as you usually would. Power the system up at the mains and try switching it on. If this works it could be time for a good clean of the switch, or better still a new replacement.


Without carrying out more in depth tests on the CPC, it's going to be a case of shooting blindly into the dark and hope you get lucky, which is still possible at the moment. I don't think I have ever known a case of a CPC being permanently destroyed by simply powering it down.


However, a weird thing once happened with my 464. I was given it as a Christmas gift and sat for many hours ion the floor next to the tree playing head over heals. When my back had begun to crumble as a result I carefully removed the 64k expansion and Disk interface and set it up again on the kitchen table where to my horror the machine wouldn't power up, after several failed attempts I wiggled the expansions and turned it back on and got a corrupted Amsdos screen. Signs of life are always good, so I decided to give the expansion a clean but before I had the chance I noticed a piece of tinsel had become jammed in the 64k expansion connector. I was sceptical that this would be the cause as I believed it was just really a piece of shiny plastic. I removed it (with a fork of all things) and tried again and it worked perfectly! Even Christmas tat has enough conductance it seems scupper things.


The gist of this rather long winded tale is, there aren't any ancient pieces of tinsel hiding in there somewhere? Lol you never know!

[Bryce]

I assume you've measured the voltage somewhere on the board at this stage? Are the logic ICs / CPU etc getting 5V? The fact that the tape deck turns but the computer doesn't run, would suggest that the expected 5V is maybe only 4V or less. This can be due to dirt on the power socket or power switch. It is unlikely that it is a broken track, that would at least result in junk being displayed on the screen.

Bryce.

[ralferoo]

Also, check that the voltage from the monitor is correct. I guess it's possible for there to be a short on some of the windings on the transformer...

Also, you can easily bypass the switch and all the tape side circuitry by unplugging the connector that goes from the tape board to the mainboard and shorting out the appropriate pins. Make sure not to short 5V and GND though or you probably will hurt the monitor, but this could be a useful test to see if it's the tape player or the mainboard that has the fault.

[Bryce]

The 5V output from the monitor is regulated, so it would either supply 5V or nothing, so if there is a voltage drop, then it's happening in the CPC, not the monitor. I suspect it could be a capacitor with a low internal resistance.

Bryce.

[Spirantho]

Pardon me if this counts as spamming - but I do Spectrum repairs as part of my business.... and of course I also dabble in other machines.


I can certainly fix it for you but as it's my business rather than just my hobby, I'd have to charge the standard £30 + parts fee I'm afraid.
Let me know if my services could be useful though.
(If this advertising of my shop service is against the terms of the forum could an admin let me know please and I won't do it again. )

[Bryce]

If you were plugging something non-cpc / retro I could understand there being rules against it. But I don't think anyone here would have something against you letting your services be known, when it's something that could be a benifit to many here.

That's my opinion at least.

Bryce.

[steve]

It is important to know who can do repairs and where they are located, maybe you could post about your services in the classified section.

[endangermice]

I think it's great that your advertising your services, there are many people out there who wouldn't know where to start and who have become very attached to their machines over the years. When they do pack in, it feels like you've lost an old friend. Having people around who can bring them back to life can only be a good thing besides which I'm looking forward to you posting some more repair stories on your blog! I'm still working on mine (which includes an Archimedes A3000 and 6128 repair). Unfortunately I have loads of other work to do at the same time so things are progressing slower than I'd like but I will get there!

[Gryzor]

Certainly not a problem with advertising one's services as long as they're relevant. People need it.